Fasting is a time-honored spiritual practice in many cultures, one which could prove to offer physical benefits as well.
There is currently considerable public and scientific interest in determining whether intermittent fasting—or intentional periods of dietary restriction—may offer a potentially effective approach for weight management and improving health.
An overview of the topic and summary of the existing research was recently published in the Annual Review of Nutrition. “Metabolic Effects of Intermittent Fasting” categorized the various regimens as:
- Complete alternate-day fasting - alternating days of regular intake with days of eating no energy-containing foods or beverages
- Modified fasting - consumption of only 20 to 25 percent of energy needs over several fasting days, alternating with regular intake during non-fasting days
- Time-restricted feeding - limiting consumption to a specific timeframe every day
- Religious fasting - various regimens undertaken for religious or spiritual purposes
Though human studies were limited, the review offered encouragement and recommendations for further research. The authors’ findings provided some support to theories that intermittent fasting regimens might improve metabolism, result in weight loss, reduced risks of obesity and obesity-related conditions, as well as chronic diseases such as diabetes and cancer.
The authors note that “even a single fasting interval (e.g., overnight) can reduce basal concentrations of metabolic biomarkers associated with chronic disease such as insulin and glucose." Their review also suggested that, unlike long fasts, intermittent fasting regimens “are not harmful physically or mentally (i.e., in terms of mood) in healthy, normal weight, overweight or obese adults.” Prolonged fasts have known risks, including fatigue, weakness, headaches, low blood sugar, electrolyte abnormalities and nutrient deficiencies.
Large-scale clinical trials are required to further determine the best fasting regimens, and more research is needed to better clarify the effects of energy intake, physical activity, sleep, gut bacteria and other factors.
So, while intermittent fasting cannot be confidently recommended for long-term health benefits at this time, the possibility is one of compelling interest. Relatively simple strategies, such as minimizing night-time eating and extending the overnight fast, might represent simple new approaches to help fight disease and build wellness—giving us a new perspective on an ancient practice.
So, for those who wish to try intermittent fasting, what might be a reasonable approach?
Confine energy intake to a 12-hour time period most days of the week
For most of us, that just means avoiding night-time snacking. If your schedule allows, shift heavier intake to earlier in the day.
Drink ample fluids during the fasting period; these can include unsweetened teas, black coffee, clear broth, plain seltzer and regular water.
Maintain a healthy diet
Whether fasting or not, eating a whole-foods, anti-inflammatory diet such as the Mediterranean diet remains one of the best known ways to reduce your risk of many chronic diseases.
Consult with your health care provider
Fasting is not recommended for pregnant or breast-feeding women; children; diabetic individuals on insulin; or people who have eating disorders, are underweight or who have certain other medical conditions.
Your primary care provider or registered dietitian can answer more specific questions about your particular dietary needs.